Cooling systems of motor vehicle engines are customarily equipped with a thermostatic valve, which controls the distribution of the amounts of a coolant exiting the internal combustion engine and flowing through a coolant radiator back to the internal combustion engine or, bypassing the coolant radiator, directly through a bypass back into the engine. It is attempted by means of this thermostatic valve to maintain the operating temperature of the internal combustion engine at as constant (high) a temperature as possible after it has warmed up.
Thermostatic valves of this type have achieved a very high standard of quality because of long years of development, so that they fail only rarely. Still, there is the need for monitoring the ability of the thermostatic valve to function.